Re: mkisofs mastering sparse files - end result file full of zeros

[Thomas Schmitt]

Hi,

Graham Leggett wrote:
> Using mkisofs as packaged on Redhat Enterprise 9

They really should not simply call xorrisofs "mkisofs" ...


> It seems to be true that:
> - attempting to burn a sparse file doesn't work; and
> - no errors, no warnings; and
> - you just end up with a sparse file of the same virtual size as the
> original file containing purely zeros.
>
> Is this a known problem?

No. Usually a reading program should see no difference between a sparse
file and a file that contains really written 0-bytes instead of the holes.

I made a mini test on an ext4 filesystem:

  $ echo hello | dd bs=1 seek=1G of=1gb_sparse
  6+0 records in
  6+0 records out
  6 bytes (6 B) copied, 0.0372587 s, 0.2 kB/s
  $ ls -l 1gb_sparse
  -rw-r--r-- 1 ... ... 1073741830 Nov 24 15:57 1gb_sparse
  $ du 1gb_sparse
  4       1gb_sparse

So my test file ist very sparse.

  $ xorriso-1.5.4 -as mkisofs -o test.iso --for_backup 1gb_sparse
  GNU xorriso 1.5.4.pl02 : RockRidge filesystem manipulator, libburnia project.
  ...
  ISO image produced: 524474 sectors
  Written to medium : 524474 sectors at LBA 0
  Writing to 'stdio:test.iso' completed successfully.

  $ sudo mount test.iso /mnt/iso
  mount: /dev/loop0 is write-protected, mounting read-only
  $ diff /mnt/iso/1gb_sparse 1gb_sparse
  $

No difference.

  $ dd bs=1 skip=1G if=1gb_sparse
  hello
  $ dd bs=1 skip=1G if=/mnt/iso/1gb_sparse 1gb_sparse
  hello
  $

So the "hello" is in the ISO filesystem, too.

What happens if you try above program runs on your machine ?


--------------------------------------------------------------------
If you have doubts about version 1.5.4 versus 1.5.4.pl02:

GNU xorriso 1.5.4.pl02 is supposed to have the same source code and
functionality as dynamically linked xorriso-1.5.4 using libisofs-1.5.4,
libburn-1.5.4 and libisoburn-1.5.4.
It is available from
  https://ftp.gnu.org/gnu/xorriso/xorriso-1.5.4.pl02.tar.gz
with GPG signature file
  https://ftp.gnu.org/gnu/xorriso/xorriso-1.5.4.pl02.tar.gz.sig
which should yield with gpg --verify:
  Primary key fingerprint: 44BC 9FD0 D688 EB00 7C4D D029 E9CB DFC0 ABC0 A854
The public key can be fetched by
  gpg --keyserver keyserver.ubuntu.com --recv-keys ABC0A854

Compilation instructions are in its README. Essentially what is written in
  https://www.gnu.org/software/xorriso/README_xorriso
with "1.5.4" instead of "1.5.6".

The reason for ".pl02" was a bug in libisofs which was discovered after
GNU xorriso-1.5.4 was uploaded but before libisofs-1.5.4 was published.
It has nothing to do with sparse files.


Have a nice day :)

Thomas